1. Field of the Invention
The present invention relates to motors with oil dynamic pressure bearings, which are equipped with a rotary shaft and a dynamic pressure bearing member in which the rotary shaft rotates relatively to the dynamic pressure bearing member in a non-contact manner, oil dynamic pressure bearing devices and method for manufacturing the same. The present invention also relates to motors with oil dynamic pressure bearing and oil dynamic pressure bearing devices, which can be used for disk drive motors for magnetic disks, optical disks or the like, as well as drive motors of a variety of apparatuses for which high rotational precision is demanded.
2. Related Background Art
Motors with oil dynamic pressure bearing (hereafter referred to as “oil dynamic pressure bearing motors”) are used as drive motors for various apparatuses for which high rotational precision is demanded. For example, in hard disk drive apparatuses, the recording density of hard disks is increasing rapidly, and the rotational speed and rotational precision of disks are concomitantly on the rise. Using oil dynamic pressure bearing motors with oil dynamic pressure bearing apparatuses is an appropriate approach to meet demands for higher rotational speed and higher rotational precision of disks.
Lengthening the joining length between members that are mutually joined is effective for achieving higher rotational speed and higher rotational precision of oil dynamic pressure bearing motors, and ensuring longer bearing range in the axial direction of radial dynamic pressure bearings is effective for obtaining higher rigidity for the dynamic pressure bearings. On one hand, it is desirable to structure dynamic pressure bearing motors to seal sufficient amount of lubricating oil to maintain a long life for the dynamic pressure bearing motors, while on the other hand it is desirable to provide sealing apparatuses, which prevent the lubricating oil from leaking, with ample space.
FIGS. 11 and 12 indicate examples of oil dynamic pressure bearing motors that may satisfy demands described above. The oil dynamic pressure bearing motors shown in FIGS. 11 and 12 will be described below. In FIGS. 11 and 12, the emphasis is on the dynamic pressure bearing part, and the motor part is omitted.
In FIG. 11, a rotary shaft 16 is rotatively supported by a dynamic pressure bearing member 14. The dynamic pressure bearing member 14 is virtually cylindrical, and the rotary shaft 16 is fitted into its center hole with a miniscule gap between the two members. On the part of the rotary shaft 16 that protrudes above the top end of the dynamic pressure bearing member 14 is joined a rotary member 20 through press fit. In this example, the rotary member 20 is a hub that rotates with a disk mounted on it. To prevent lubricating oil 18 that generates dynamic pressure force from leaking out, joining parts between the rotary shaft 16 and the rotary member 20 are welded, or sealed by a scaling material, along the entire circumference. The dynamic pressure bearing member 14 comprises a cylindrical section, which forms radial dynamic pressure bearings 26, 26, and an expanded diameter section 28, which forms a thrust dynamic pressure bearing 34 on the outer circumference side of the cylindrical section. The expanded diameter section 28 is formed as a flange on one end section (in the figure, on the left end section) of the cylindrical section. On the inner circumference surface of the cylindrical section of the dynamic pressure bearing member 14, radial dynamic pressure generating grooves are formed. Thrust dynamic pressure generating grooves are formed on an end surface of the expanded diameter section 28. The radial dynamic pressure generating grooves are formed along the entire circumference at two locations separated from each other on the inner circumference surface of the cylindrical section of the dynamic pressure bearing member 14. The thrust dynamic pressure generating grooves are also formed along the entire circumference on the end surface of the expanded diameter section 28.
Into the cylindrical section of the dynamic pressure bearing member 14 is inserted from above the rotary shaft 16 that is press fit in a unitary fashion with the rotary member 20. From the bottom on the outer circumference of the dynamic pressure bearing member 14 a ring-shaped fallout preventing member 30 is inserted and joined to an inner circumference surface 54 of the rotary member 20 The rotary member 20 has a flat step section 56 that is continuous with the inner circumference surface 54, and the fallout preventing member 30 is joined also to the step section 56. Furthermore, to prevent the lubricating oil 18, to be described later, from leaking, a joining section between the fallout preventing member 30 and the rotary member 20 is Sealed with an adhesive. At the bottom end of the dynamic pressure bearing member 14 is formed a concentric circumferential groove 100 along the entire circumference, as described later (see FIG. 13), and a flat-shaped cover 22 is capped on the circumferential groove 100, such that the bottom end opening of the dynamic pressure bearing member 14 is closed off by the cover 22. The cover 22 is sealed with an adhesive 24 in the circumferential groove 100 at the bottom end of the dynamic pressure bearing member 14.
A gap is formed between the inner circumference surface of the fallout preventing member 30 and the opposing outer circumference surface of the dynamic pressure bearing member 14, between the top surface of the fallout preventing member 30 and the opposing bottom surface of the expanded diameter section 28 of the dynamic pressure bearing member 14, between the outer circumference surface of the expanded diameter section 28 and the opposing circumferential wall surface of the rotary member 20, between a ceiling surface of the rotary member 20 and the opposing top surface of the expanded diameter section 28, between the inner circumference surface of the dynamic pressure bearing member 14 and the opposing outer circumference surface of the rotary shaft 16, and between the cover 22 and the bottom end surface of the rotary shaft 16.
These gaps are mutually communicated with each other in the sequence described above and are filled with the lubricating oil 18. The gap between the inner circumference surface of the fallout preventing member 30 and the opposing outer circumference surface of the dynamic pressure bearing member 14 is open towards the bottom. Further, the outer circumference surface of the dynamic pressure bearing member 14 that opposes the inner circumference surface of the fallout preventing member 30 is a tapered section whose outer diameter grows smaller towards the bottom; as a result, the gap between the inner circumference surface of the fallout preventing member 30 and the outer circumference surface of the dynamic pressure bearing member 14 forms a capillary sealing section 32 whose dimension gradually enlarges towards the bottom. The liquid level of the lubricating oil 18 is in the capillary sealing section 32.
The lubricating oil 18 is poured into the gaps through the capillary sealing section 32. The thrust dynamic pressure bearing 34 is formed between the end surface of the rotary member 20 on the side of the expanded diameter section 28 and the opposing end surface of the expanded diameter section 28, and the radial dynamic pressure bearings 26, 26 are formed at two locations separated from each other between the inner circumference surface of the dynamic pressure bearing member 14 and the outer circumference surface of the rotary shaft 16. The lubricating oil 18 is present in these dynamic pressure bearings.
The outer circumference of approximately half of the bottom of the dynamic pressure bearing member 14 is fitted and fixed to the inner circumference side of a cylindrical section formed in the center section of a base plate 10, which is indicated by a dotted line. The cylindrical section of the base plate 10 extends into the rotary member 20 to reach near the fallout preventing member 30. In FIG. 11, L represents the joining length in the axial direction between the base plate 10 and the dynamic pressure bearing member 14.
At the bottom end of the rotary member 20 is formed a cylindrical circumferential wall 44, and a drive magnet, not shown, is mounted on the outer circumference surface of the circumferential wall 44. The drive magnet, the rotary member 20 and the rotary shaft 16 make up a rotor of the motor. In the meantime, on the base plate 10 is fixed a stator of the motor consisting of a core and drive coils wound around a plurality of salient poles formed in a unitary structure with the core, all not shown. The salient poles of the stator oppose the outer circumference surface of the drive magnet across an appropriate gap, and the rotor is rotatively driven by switching the energization provided to the drive coils.
The example shown in FIG. 12 has a structure virtually identical to the example in FIG. 11, but the thickness of a fallout preventing member 30, the length of a capillary sealing section 32, and a length L of a joining section between a dynamic pressure bearing member 14 and a base plate 10 are different. In the example shown in FIG. 11, the joining length between the rotary shaft 16 and the rotary member 20, the thickness of the fallout preventing member 30, and the length of the capillary sealing section 32 are all amply provided for, but the length L of the joining section between the dynamic pressure bearing member 14 and the base plate 10 is not sufficient. The example in FIG. 12 amply provides for a joining length between a rotary shaft 16 and a rotary member 20 and the joining length L of the joining section between the dynamic pressure bearing member 14 and the base plate 10, but the thickness of the fallout preventing member 30 and the length of the capillary sealing section 32 are insufficient; consequently, the amount of lubricating oil retained is small and there is a risk of shortening the life of the motor as a result of the evaporation of the lubricating oil. Furthermore, the joining strength between the base plate 10 and the dynamic pressure bearing member 14 is also insufficient.
In the meantime, an oil dynamic pressure bearing apparatus used in the oil dynamic pressure bearing motor is provided with a rotary shaft and a dynamic pressure bearing member, and lubricating oil is present in a minuscule gap between the rotary shaft and the dynamic pressure bearing member. By having the rotary shaft rotate relatively to the dynamic pressure bearing member, dynamic pressure force is generated by dynamic pressure generating grooves formed at least on one of the rotary shaft and the dynamic pressure bearing member, and the dynamic pressure force causes the rotary shaft to rotate without any contact with the dynamic pressure bearing member.
An example of the oil dynamic pressure bearing apparatus used in the oil dynamic pressure bearing motor in FIG. 11 is shown in FIG. 13. In FIG. 13, radial dynamic pressure generating grooves 74, 74, which compose parts of a radial dynamic pressure bearing, are formed on both end sections in the axial direction of a surface of a rotary shaft insertion hole of the generally cylindrical dynamic pressure bearing member 14. The rotary shaft, not shown, is inserted in the rotary shaft insertion hole of the dynamic pressure bearing member 14 with a minuscule gap between it and the surface of the rotary shaft insertion hole. In FIG. 13, on the top end surface of the dynamic pressure bearing member 14 are formed the circumferential groove 100, except for a circular dyke 102, i.e., a circular wall, on the outer circumference. A cover 22 is placed in the circumferential groove 100. The cover 22 is flat cup-shaped and has a cylindrical circumferential wall 221, as well as a flange section 222 that is continuous with the circumferential wall 221 and protrudes perpendicularly outward from the circumferential wall 221. With the flange section 222 in contact with the bottom surface of the circumferential groove 100, the adhesive 24 is filled into and hardened in the circumferential groove 100; this causes the cover 22 to be fixed to the dynamic pressure bearing member 14, such that one end surface of the dynamic pressure bearing member 14 whose rotary shaft insertion hole is open is closed off by the cover 22.
As indicated in FIG. 11, the dynamic pressure bearing member 14 is vertically inverted from its posture shown in FIG. 13. The inner diameter of the circumferential wall 221 of the cover 22 is the same as the inner diameter of the dynamic pressure bearing member 14, such that when the rotary shaft 16 is inserted into the rotary shaft insertion hole of the dynamic pressure bearing member 14, an end section of the rotary shaft 16 enters into the cover 22. There is a minuscule gap between the inner circumference surface of the circumferential wall 221 of the cover 22 and the outer circumference surface of the rotary shaft 16. Further, due to the fact that a rotary body including the rotary shaft 16 is supported in the thrust direction by the thrust dynamic pressure bearing 34, there is a minuscule gap also between one end surface of the rotary shaft 16 and the opposing inner bottom surface of the cover 22. The lubricating oil 18 is present in these gaps, so that when the rotary shaft 16 rotates relatively to the dynamic pressure bearing member 14, dynamic pressure force is generated by the radial dynamic pressure generating grooves 74, 74 and the rotary shaft 16 is supported without any contact with the dynamic pressure bearing member 14.
Another example of an oil dynamic pressure bearing apparatus is shown in FIG. 14. In FIG. 14, around the periphery of an opening section of a rotary shaft insertion hole on one end surface of a dynamic pressure bearing member 14 is formed a groove-shaped circumferential groove 76 that is depressed in the axial direction and continuous in the circumferential direction. Into the circumferential groove 76 is inserted a cylindrical circumferential wall 221 of a flat cup-shaped cover 22, such that one end surface of the dynamic pressure bearing member 14 whose rotary shaft insertion hole is open is closed off by the cover 22. The outer circumference surface of the circumferential wall 221 of the cover 22 is in contact with a circumferential wall surface on the outer diameter side of the circumferential groove 76; an adhesive is filled and hardened on the contact surfaces, which provides a seal to prevent lubricating oil from leaking.
In recent years, there are increasingly greater demands to make hard disk drive apparatuses and other apparatuses even smaller and thinner, and demands to make oil dynamic pressure bearing motors thinner have grown stronger along with them. For example, super-thin type hard disk drive apparatuses, which may be called card-compatible hard disk drive apparatuses, are close to being realized, and the height of motors used in such hard disk drive apparatuses would have to be limited to approximately 3 mm. When an attempt is made to realize such an oil dynamic pressure bearing motor, whose height dimension is extremely limited, using structures indicated in FIG. 11 or 12, problems described below can occur.
When the rotary member 20 and the rotary shaft 16 are joined, if the perpendicularity precision of both members is poor, the swing of the rotary member 20 during rotation becomes larger. In the case of a disk drive motor, a disk mounting surface swings and causes the disk to undulate as it rotates, such that the disk vibrates, or the flow of air generated by the rotation of the disk becomes disrupted. Any of these can cause the head to fail to levitate above the disk by a predetermined amount and/or tracks to be displaced and error rate during data reproduction to be increased. Further, due to the fact that the back surface of the rotary member 20 is a thrust bearing surface, if the perpendicularity of the rotary shaft 16 with the rotary member 20 is poor, the number of revolutions for levitation, i.e., the number of revolutions required to obtain predetermined levitating force in the thrust direction, increases, such that the amount of time the rotary member 20 is in contact with the dynamic pressure bearing member 14 becomes longer, which causes greater bearing wear and therefore lower reliability of the bearing.
In the meantime, in order to ensure the perpendicularity between the rotary member 20 and the rotary shaft 16, the joining length between the two must be equal to or greater than a predetermined length.
Next, the height, i.e., the length in the axial direction, of the dynamic pressure bearing member 14 will be considered. The outer circumference section of the dynamic pressure bearing member 14 must accommodate the thickness dimension of the expanded diameter section 28, the length that corresponds to the fallout preventing member 30, the length of the capillary sealing section 32, and the joining length between the base plate 10 and the dynamic pressure bearing member 14. The joining length between the base plate 10 and that dynamic pressure bearing member 14 requires a joining strength that would not cause the members to move or separate even if there is impact or vibration applied from the outside. Normally, since the base plate 10 and the dynamic pressure bearing member 14 are joined by an adhesive, sufficient joining area must be ensured.
When demands for thinner motors become more and more vigorous as they have been in recent years, dynamic pressure bearing motors, in which the thrust dynamic pressure bearing 34 is virtually in the same position in the axial direction as the position of an end section of the radial dynamic pressure bearings 26 as in the examples in FIGS. 11 and 12, face circumstances in which they cannot satisfy demands using the structures of examples indicated in FIGS. 11 and 12. In other words, when the joining length between the rotary shaft 16 and the rotary member 20, the thickness of the fallout preventing member 30 and the length of the capillary sealing section 32 are amply provided for as in the example in FIG. 11, the length L of the joining section between the dynamic pressure bearing member 14 and the base plate 10 cannot be sufficiently ensured. When the joining length between the rotary shaft 16 and the rotary member 20 and the length L of the joining section between the dynamic pressure bearing member 14 and the base plate 10 are amply provided for as in the example in FIG. 12, the thickness of the fallout preventing member 30 and the length of the capillary sealing section 32 cannot be sufficiently ensured.
Further, as shown in FIG. 13, the cover 22 that closes off one end surface of the dynamic pressure bearing member 14 is flat cup-shaped and fixed through adhesion to the circumferential groove 100 formed on one end surface of the dynamic pressure bearing member 14, and one part of the rotary shaft 16 is inserted into the cover 22. For this reason, the effective length in the axial direction of the dynamic pressure bearing member 14 is limited by the depth of the circumferential groove 100, which causes the span of the top and bottom radial dynamic pressure bearings to be shorter, which in turn causes the oil dynamic pressure bearing apparatus to tend to have low rigidity. On the other hand, when the span of the top and bottom radial dynamic pressure bearings is lengthened in an effort to ensure rigidity for the oil dynamic pressure bearing apparatus, the dynamic pressure bearing member 14 becomes longer and the oil dynamic pressure bearing motor cannot be made thinner. However, there is an advantage in that the joining length between the dynamic pressure bearing member 14 and the base plate 10 can be sufficiently ensured. In addition, the structure allows the adhesive 24 to easily enter the bearing, i.e., into the rotary shaft insertion hole.
In the meantime, as shown in FIG. 14, since the cover 22 closes off an opening on virtually one and surface of the dynamic pressure bearing member 14, the effective length of the dynamic pressure bearing member 14 becomes longer; this makes it possible to provide for a long span of the top and bottom radial dynamic pressure bearings, which is advantageous for obtaining an oil dynamic pressure bearing apparatus with high rigidity. In addition, there is another advantage in that this can ensure sufficient joining length between the dynamic pressure bearing 14 and the base plate 10. However, due to the fact that the outer circumference surface of the cover 22 and the outer circumferential wall surface of the ring-shaped circumferential groove 76 formed on one end surface of the dynamic pressure bearing member 14 are joining surfaces, sufficient adhesive cannot be coated on or filled in between the dynamic pressure bearing member 14 and the cover 22; this results in insufficient reliability for a sealing means of the opening. Furthermore, a large space formed between the circumferential wall 221 of the cover 22 and the wall surface on the inner circumference side of the circumferential groove 76 must be filled with dynamic pressure generating lubricating oil, which requires a long time and leads to lower productivity. Moreover, parts that are filled with a large amount of the lubricating oil tend to have air bubbles in the lubricating oil, which can cause the lubricating oil to be more prone to leaking.
In addition to the examples described, the sealing structure of one end surface of the dynamic pressure bearing member 14 can be as shown in FIGS. 15 through 17.
In the example in FIG. 15, a circumferential groove 88 is formed on one end surface of a dynamic pressure bearing member 14, a flat plate-shaped cover 86 is mounted on the circumferential groove 88, and a circumferential edge of the cover 86 and a circumferential edge of the circumferential groove 88 are welded together with a laser welder 90. In this example, the thickness of the cover 86 must be thick in order to achieve high reliability for the sealing means of an opening, but the thicker cover 86 causes the span in which to position a radial dynamic pressure bearing 14 to be shorter.
In the example in FIG. 16, a shallow concavely depressed section is formed on one end surface of a dynamic pressure bearing member 14, a groove-shaped circumferential groove 94 that is depressed in the axial direction and continuous in the circumferential direction is formed on the outer circumference side of the concavely depressed section, a thin flat plate-shaped cover 92 is placed over the shallow concavely depressed section, an adhesive 24 is filled in the circumferential groove 94, and an outer circumference edge section of the cover 92 is adhered to the dynamic pressure bearing member 14 to seal an opening. In this examples, the outer circumference edge section of the cover 92 is not folded and the flat plate-shaped cover 92 is joined to the dynamic pressure bearing member 14 through adhesion. For this reason, the liquid level of the adhesive 24 is in the same position as an end surface of the opening of the dynamic pressure bearing member 14, which causes the adhesive 24 to tend to flow into a rotary shaft insertion hole and interfere with a rotary shaft.
In the example in FIG. 17, a cylindrical dyke 108 is formed on the outer circumference of one end section of a dynamic pressure bearing member 14, a groove-shaped circumferential groove 98 that is depressed in the axial direction and continuous in the circumferential direction is formed along the inner circumferential wall of the dyke 108, a flat plate-shaped cover 92 is fitted on the inner circumference side of the dyke 108, an adhesion 24 is filled in the circumferential groove 98, and the adhesive 24 is coated between an outer circumference edge section on the front surface of the cover 92 and the inner circumferential wall of the dyke 108 to fix the cover 92 to the dynamic pressure bearing member 14. According to this example, due to the fact that one end section of the dynamic pressure bearing member 14 is depressed to form the dyke 108, the dimension in the axial direction to form radial dynamic pressure bearings is limited by the height of the dyke 108, which reduced the rigidity of the dynamic pressure bearing.